Process of making porous, bonded fibrous web

ABSTRACT

Sheets comprising fibrous materials which are soft, excellent in mechanical properties, smooth at the surface thereof, and high in air and moisture permeability are produced by the steps of 1. BONDING FIBER WEBS WITH ANOTHER USING A BINDER (A) having plasticizing or molding ability at a temperature lower than a melting point or degrading temperature of the fibers constituting the fiber webs, 2. BONDING FURTHER THE WHOLE WEBS TOGETHER BY IMPREGNATING OR FILLING THE INTERSTICES REMAINING WITH THE MOLDED WEBS WITH A BINDER (B) without dissolving or swelling the constituent fibers and the binder (A), and 3. DISSOLVING THE BINDER (A) to remove therefrom using a solvent which dissolves the binder (A) but not the constituent fibers and the binder (B). As the binder (A), there may be used starch, dextrin, carboxymethylcellulose, methylcellulose, casein, polyethylene oxide, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate or the like. As the binder (B), there may be polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyamide, polyester, polyacrylate, polyurethane, synthetic rubber of every kind, natural rubber or the like.

United States Patent [7 2] Inventors Shigeru Ishida Fukaya, Saitama; Masayuki Yonei, Fukaya, Saitama; Tadashi Yokota, Kyoto, all of Japan [211 App]. No. 732,550 [22] Filed May 28, 1968 [45] Patented Nov. 9, 1971 [73] Assignee Nippon Cloth Industry Co., Ltd. Kyoto, Japan [54] PROCESS OF MAKING POROUS, BONDED FIBROUS WEB 4 Claims, No Drawings [52] US. Cl 156/77, 117/76 T, 156/83, 156/148, 156/155, 161/81, 161/227, 161/D1G. 2 [51] Int. Cl B32b 5/18 [50] Field of Search 156/77, 83,

[56] References Cited UNITED STATES PATENTS 2,994,617 8/1961 Proctor l56/77X 3,477,898 11/1969 Buffet a1. 156/148 X 3,486,968 12/1969 Mater l56/77X Primary Examiner- Leland A. Sebastian Attorney-Waters, Roditi & Schwartz ABSTRACT: Sheets comprising fibrous materials which are soft, excellent in mechanical properties, smooth at the surface thereof, and high in air and moisture permeability are produced by the steps of l. bonding fiber webs with another using a binder (A) having plasticizing or molding ability at a temperature lower than a melting point or degrading temperature of the fibers constituting the fiber webs,

2. bonding further the whole webs together by impregnating or filling the interstices remaining with the molded webs with a binder (B) without dissolving or swelling the constituent fibers and the binder (A), and

3. dissolving the binder (A) to remove therefrom using a solvent which dissolves the binder (A) but not the constituent fibers and the binder (B),

As the binder (A), there may be used starch, dextrin, carboxymethylcellulose, methylcellulose, casein, polyethylene oxide, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetate or the like. As the binder (B), there may be polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyamide, polyester, polyacrylate, polyurethane, synthetic rubber of every kind, natural rubber or the like.

PROCESS OF MAKING POROUS, BONDED FIBROUS WEB The present invention relates to a sheet comprising fibrous material and to a process for producing the same. More particularly, the invention pertains to a sheet comprising fibrous materials, which is soft, excellent in mechanical properties, smooth at the surface thereof and high in air and moisture permeability, and to a process for producing the same.

The so-called sheets comprising fibrous materials have heretofore been produced by preparing webs according to a process which comprises carding fibers of every kind with a card or garnet and stacking fibers at random according to the air floating method, if necessary subjecting the resulting webs to mechanical bonding such as needle punching or felting treatment, and then banding the fibers with one another using a binder. The sheets comprising fibrous materials prepared in the above manner may vary in properties depending on various conditions, such as the method employed for forming webs, the presence of needle punching or felting treatment, or degree thereof, the kind of binders as well as fibers employed, the ratio of fibers to binder or the method of use of the binder to be employed. In every case, however, because of adhesion directly effected between the fibers and binder, when the amount of binder is increased to improve mechanical strength,

softness and drapability become poor. To the contrary, the amount of binder must be controlled in order to improve softness, and therefore the lowering in mechanical strength is unavoidable. Thus, it is difficult to possess soft hand simultaneous with sufficient mechanical strength. Particularly, it is extremely difficult to produce such a sheet comprising fibrous material, which has both soft hand, and mechanical strength, and also has excellent gas and moisture permeability, as comparable to natural leather in the uses as a substitute thereof or a substrate of synthetic leather.

Generally, for the purpose of improving strength of a sheet comprising fibrous materials, it is desirable to make density of the fibers high in the sheet comprising fibrous materials by selecting such fibers high in tenacity of single fiber and having suitable fiber length and denier. As regards the binder, it is necessary to suitably select the kind of binders employed and the amount of the binder applied. However, in the ordinary processes for producing sheets comprising fibrous materials, there is a limit in density of stacked fibers structure because of bulkiness own by the fibers themselves, and therefore the density of the stacked fiber structure does not sufficiently increase even when the fibers are bonded together with a binder. Furthermore, when a sheet comprising fibrous material to which a binder has been applied is pressed at a temperature higher than a softening point of the binder resin, density of the sheet is increased due to molding characteristic of the binder resin, thereby to improve bonding power of the sheet comprising fibrous materials. However, softness ofthe sheet is lost and hand is degraded, and at the same time the binder fills up the interstices among the fibers, which is liable to a hinderance to air and moisture permeability.

Accordingly, it is an object of the present invention to provide a sheet comprising fibrous material, in which such difficult problems as mentioned above, i.e. softness and mechanical strength of sheet comprising fibrous materials can be consistent with each other, having high air and moisture permeability and efficiencies comparable to natural leather, and to provide a process for producing the same.

As the fibers used as raw material in the sheet comprising fibrous materials in accordance with the process of the present invention and in the present process, any of the fibers for use in spinning and weaving, such as natural fibers, and synthetic fibers, used in ordinary sheets comprising fibrous materials may be used except for such fibers soluble in specific solvents as described later. That is, webs are prepared using such natural fibers, synthetic fibers or mixed fibers thereof by a card, garnet or an apparatus according to the air floating method, if necessary the resultant webs are subjected to mechanical bonding treatment such as needle punching or felting treatment, and then a solution, emulsion, dispersion or the like of a binder (A) having molding characteristic at a temperature lower than a melting point or degrading temperature of the fiber is applied onto the thus obtained fiber mat in such a manner that the amount of the binder applied in terms of solid form is within the range as described later to bond the fiber webs with one another. Subsequently, the thus bonded mat is pressed using an apparatus such as a flat press machine, roll press machine or belt press machine heated to a temperature above a softening point of the binder (A) to put into shape with such a thickness in such manner that density of the stacked fiber structure in the webs is within such given values as described later. Subsequently, the pressed mat is impregnated with a solvent solution, emulsion, dispersion or the like of a high molecular binder (B) which does not dissolve or swell the binder (A), and the whole webs are further bonded together by means of drying with heat or coagulation of the binder. Then, the binder (A) is dissolved and removed therefrom by treating the bonded webs with a solvent which dissolves the binder (A) but not the binder (B) and the constituent fibers, whereby the aimed sheet comprising fibrous materials can be obtained.

In the sheet comprising fibrous materials obtained in accordance with the present process, the constituent fibers maintain the density of the stacked fiber structure established beforehand, and because the interstices, which have formerly occupied by the binder (A), are present between the binder (B), i.e. the final binder used in the sheet comprising fibrous material, and the fibers, adhesion between the fibers and binder is not effected at least at the portions of said interstices. Accordingly, when external stress is applied to the present sheet comprising fibrous materials, sliding movement is caused between the fibers and binder, whereby soft hand is brought about, and at the same time a nonrupturing displacement within the system against external force is liable to take place whereby excellent efficiencies in mechanical strengths can be displayed together with high density of the stacked fiber structure. Furthermore, because air can be circulated through both sides of the sheet by passing through the interstices formed along the surface of the fibers, and at the same time a large portion of surface area of the fiber is not directly coated with the binder, hygroscopic property inherently owned by the fibers is not obstructed, and moisture absorbed by the fibers can be purged without disturbance. Furthermore, because of molding characteristic of the binder (A), the surface of the sheet comprising fibrous materials obtained in accordance with the present process can precisely be duplicated with smoothness of the surface of pressing body such as a flat press machine, roll press machine or belt press machine. Therefore, the present sheet can be provided with suitable smoothness simultaneous with uniform thickness as a substrate sheet comprising fibrous materials for effecting the secondary processings such as coating and the like, for example. That is, the sheet comprising fibrous materials obtained according to the present process is characterized in that it has soft hand simultaneous with excellent mechanical strengths with smooth surface and uniform thickness, and high in air and moisture permeabilities. The process of the present invention is further explained below.

In the present process. density of the stacked fiber structure in the bonded webs at the stage where the bonding with the binder (A) and subsequent pressing have all been completed. is to determine density of the stacked fiber structures in the finished sheet comprising fibrous materials. This density of the stacked fiber structures in the pressed webs or the finished sheet comprising fibrous materials is defined by volume occupying ratio of the fiber component in the volume of the pressed webs or the finished sheet comprising fibrous materials in the unit area. Said volume occupying ratio of the fiber component is represented by S, in this specification. Generally, there are referred to the volume occupying ratio as S; volume per unit area as V; weight per unit area as W; specific gravity as p; thickness as d; the total as r; fiber as f; binder (A) as a; binder (B) as b; and interstice as v. Further- The binder (A) is required to have moldability when heated and pressed, and good shape-maintaining property. When such binder, the withdrawal of which, after the molding has been completed, can be effected without any difficulty, and molding conditions therefor are selected, the molded sheet having such thickness that volume occupying ratio of the fibers is within the range of from 12 to 40 percent results in a favorable incarnation of characteristic according to the present invention. That is, if the volume occupying ratio of the fibers is less than l2 percent, density of the stacked fiber structures is insufficient, whereby the desired mechanical strengths, particularly tensile strength, tear strength and anabrasion properly, become poor. Furthermore, if it is above 4 percent, density of the stacked fiber structures becomes too much, whereby hand become hard and the binder (B) becomes difficult to uniformly permeate therein. In practice, it is convenient to calculate the volume occupying ratio of the fibers according to the following equation derived from equation l) Subsequently, volume of the bonded and pressed webs is represented by the following equation:

v,= v w,,+ V,. 3

When the bonded webs is treated with the binder (B), V,,V,. must be brought since the binder (B) is filled up in V,.. In oEier to obtain the sheet comprising fibrous materials sufficiently having characteristic of the present invention, it is necessary that the volume occupying ratio of the binder (B) is to be 4 percent or more. If it is less than 4 percent, the object of the present invention cannot be satisfactorily displayed because the necessary efficiency exhibited by the binder component becomes insufficient among the properties owned by the sheet comprising fibrous materials. Furthermore, the volume occupying ratio of the fibers is within the range of from 12 to 40 percent, as previously mentioned. Accordingly, the volume occupying ratio of the binder (A) should be established to be less than 84 percent. In practice, however, the binder (B) contains volatile components such as water, organic solvent or the like in many cases. Furthermore, even when a binder which is solidified as such without changing its volume in the form of liquid, the binder (B) hardly occupies the interstices in the webs perfectly. In practice, the present process exhibits its effectiveness when the volume occupying ratio of the binder (A) is within the range of from 0.5 to l percent. If, the amount of the binder (A) applied is such a value, wherein the volume occupying ratio thereofis less than 0.5 percent, shapemaintaining property due to the binder (A) is lowered, and at the same time the effect of interstices attained by removal of the binder (A) is also lowered, whereby significance of using the binder (A) is faded out. Furthermore, if the amount of the binder (A) applied is a value exceeding its volumetric ratio percent, the interstices between the binder (B) and fibers become too large, and because the binder (B) tends to be too much discrete due to the binder (A), which results in lowering dimensional stability and mechanical strengths of the resultant sheet comprising fibrous materials. From the foregoing, the volume occupying ratio of the interstices component remained in the bonded webs after pressing is preferably defined to be within the range of from 50 to 87.5 percent. That is, in bonding the fiber webs with one another with the binder (A) in accordance with the present process, when the bonded webs is pressed so that the fiber volume occupying ratio is a value selected within the range of from 12 to 40 per cent, the amount of the binder (A) applied must be controlled so that the volume occupying ratio of the binder (A) is a value selected within the range of from 0.5 to 10 percent.

Since the volume occupying ratio of the binder (A) in the bonded webs after pressing is represented by the following equation,

S,,, Vt X pXd(mm.) X 10 That is, the above equation is brought about as follows:

W.,(g'/ p" (mm-) Furthermore, from equation (2), the above equation is brought about as follows:

W,g./m. )=S, p,Xd(mm.) (7) In the production of sheet comprising fibrous material in accordance with the present invention, weight of the fiber webs to be bonded with the binder (A) is given according to equation (7), and an amount of the binder (A) applied on the basis of the said fiber webs is given by equation (6) in planning to determine quality of the desired sheet, when thickness, 11 (mm.), density of the stacked fiber structure (equivalent to volume occupying ratio) 5,, and volume occupying ratio of the interstices [equivalent to volume occupying ratio of the binder (A)]S,, to be obtained by removal of the binder (A) are established. When the above various factors are determined, quality of the sheet comprising fibrous materials to be produced is decided by the kind of binder (B) and the amount thereof employed as long as a given fiber, binder (A) and process steps are employed.

The binders (A) and (B) used in this invention may theoretically be any of those when they are used in the presence of a solvent which dissolves the binder (A) but not the constituent fibers and the binder (B). For example, as the binder (A), there may be used starch, polyvinyl alcohol, dextrin, carboxymethyl cellulose, methyl cellulose, casein, polyethylene oxide, polyvinyl chloride, polyvinyl acetate, other synthetic resins of every kind, or natural resins, singly or in combination of two kinds or more. In view of the role of the binder (A) in the present invention, it is advantageous to use such binder that is relatively inexpensive and is readily dissolved and removed by an inexpensive solvent such as water. Furthermore, as the binder (B), a solvent solution, emulsion, dispersion, fused liquid, powder, etc. of polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyamide, polyester, polyacrylate, polyurethane, synthetic rubbers and natural rubber may be used. However, in the solvent solution, emulsion or dispersion, it is necessary that the solvent or dispersing medium thereof is such that which does not dissolve or swell the binder (A) and the constituent fibers.

The following examples are given to illustrate the present invention, but should be understood they they are merely given as illustrating the invention and not as limitative.

EXAMPLE 1 In determining quality of a desired sheet comprising fibrous materials to be manufactured, the conditions therefor were specified to be as follows:

Fibers used: Mixed staple consisting of 70 parts of nylon fibers of 1.5d 38 mm. and parts of polyester fibers of 1.5d 38 mm.

Thickness of sheet: 1 mm.

Volumetric ratio of the fibers: 25 percent Volumetric ratio of polyvinyl alcohol used as the binder (A): 3 percent Specific gravity of the nylon fiber is 1.14 and the polyester 1.38, and hence the average specific gravity of the aforesaid fibers used becomes 1.20

In order to make a volume occupying ratio of this fiber component in the sheet of 1 mm. in thickness to be 25 percent, weight of the fiber webs must be 300 g./m. according to the equation (7). Furthermore, in order to make a volume occupying ratio of polyvinyl alcohol to be 3 percent, an amount of The sheet comprising fibrous materials obtained according to the above operations maintained the smooth surface with 1 mm. thickness, and had soft hand like natural leather and a uniformly smooth surface at a portion bended even when bended at a small radius of curvature. In addition thereto, the sheet had strong mechanical strength.

For comparison sake, a sheet comprising fibrous materials was prepared as a control by using the same needle-punched sheet as in this example, heat pressing the sheet into shape with 1 mm. thickness without effecting the bonding using polyvinyl alcohol and pregnating the molded sheet with the same polyurethane resin solution as in this example.

The following table shows comparison of properties of the sheet prepared in accordance with this example with those of the sheet obtained as above.

Presence of Absence of Method of binder (A) binder (A) determination Thickness (mm.) 1.0 1. 4 Mpthttid dcscrilflbed 11 1e spec cation. Weight (g./m. 410 508 Amount of urethane resin used (g./m. 110 208 Tensile sliielaglthfkg /cm width)" 13 5 l3 7 Lori u na Trar lsversenn 15.0 14.8 l X43550 Tenille stiierifithfkglrnmfiz 1 0 98 on n he Trar isverse 1.30 1.03 l K 6550 lg ll 3 1 68 61 our; u na Transverse 73 67 l K 6550 ong u Transverse 3.0 3. 7 l X43550 Teniile sliierazthfkg/mmfi): 6 3 2 orig u ina 5 q 106550 Transverse 5. 3 3.0 Soitness 34. 5 76. 5 Soltnoss lustciz Air permeability (see/100 cc.) 16 JIS P 8117. Moisture permeability (g./m. /24 hrs.) 6, J50 4,023 J IS Z 208. Smoothnoss o1 surlace.

l Seni Kako, 18 [3] 245 (1966). 2 Suitable for direct coating. 3 Coarse and uneven.

the polyvinyl alcohol applied becomes 38.78 g./m. according 40 EXAMPLE 2 to the equation (6), because a specific gravity of polyvinyl alcohol is 1.29.

Webs of the aforesaid mixed staple were prepared using a card and a cross-folder, and the webs were subjected to punching at a density of 3,000 pores/in. from both sides thereof using No. 42 barbed needles to obtain a needlepunched sheet having weight of about 300 g./m.". The resultant sheet was impregnated with a 10 percent aqueous polyvinyl alcohol solution and was then squeezed with a roll in such a manner that an amount of the solution applied becomes about 390 g./m. and then dried. The thus obtained sheet was about 2.5 mm. in thickness.

Subsequently, the sheet was pressed for 20 seconds with a flat press machine, surface temperature of both sides of which was maintained at 120 C., using together with a steel plate gauge of 1 mm. in thickness, and the pressed sheet was taken out from the press machine and cooled. The resultant pressed product had thickness of 1 mm. with a smooth surface because of thermoplasticity of polyvinyl alcohol. Subsequently, polyester obtained by reacting adipic acid with ethylene glycol was allowed to react with 4,4'-dipheny1methane diisocyanate, and the reaction product was chain extended with l-4 cyclohexanediol to obtain polyurethane elastomer the aforesaid molded webs was impregnated with a 20 percent dimethylformamide solution of the aforesaid polyurethane elastomer and was passed through a roll so as to make an amount of solution applied to be about 550 g./m. and was then dipped in water to coagulate the resin portion therein. Subsequently, this was dipped in hot water at 80 C. to perfectly extract the solvent, simultaneously to dissolve the polyvinyl alcohol which was subsequently squeezed with a roll to purge off therefrom. The operations of dipping in hot water and squeezing with a roll were repeated until color reaction of the polyvinyl alcohol with iodine was not observed any longer on the sheet, and then it was dried.

Eighty parts of nylon fibers of 1.5dX38 mm. and 20 parts of viscose rayon fibers of 1.5dX38 mm. were mixed together. The mixture was applied to a Rando Webber to obtain webs. The webs were subjected, at the both sides thereof, to punching at the density of 2,000 pores/in. to obtain a needle-punched sheet comprising fibrous materials of about 250 g./m. in weight. The sheet was impregnated with a 15 percent aqueous solution of a 1:1 mixture of dextrin and polyvinyl alcohol, squeezed with a squeezing roll, so that an amount of the aqueous solution applied is about 500 g./m. and was then dried. The resultant product was pressed for 20 seconds with a flat pressing machine, the surface temperature of which had been kept at 130 G, into a sheet of 1 mm. thickness. The pressed product was impregnated with a 1:1 mixed solution containing a 15 percent methanol solution of polyamide resin (Nylon 8) and a 15 percent dimethylformamide solution of acrylic rubber, and was squeezed with roll in such a manner that the amount of the mixed solution applied thereto was 250 g./m. and then dipped in water for 2 hours to coagulate the resin portion, simultaneously to extract the methanol and dimethylformamide. Subsequently, the resultant product was dipped in hot water at C. to dissolve the dextrin and polyvinyl alcohol, squeezed with a squeezing roll and dried. The thus obtained sheet comprising fibrous material had softness and toughness like chamois leather, which was particularly high in tensile strength, and therefore was found suitable as a substrate of synthetic leather for boots, clothes, bags and the like. The thus obtained sheet comprising fibrous materials maintained thickness of 0.9 mm. A volume occupying ratio of the fibers was 21 percent and a volume occupying ratio of the interstices caused by elution of the binder (A) was about 6 percent. 1. What is claimed is:

1. in a process for producing a sheet of fibrous materials which comprises forming webs of synthetic fibers, natural fibers or mixtures thereof and bonding the thus formed webs with one another using a binder, an improvement comprising the steps of 2. bonding the formed fiber webs with one another using a binder (a) having plasticizing ability at a temperature below the melting point or degrading temperature of the fibers constituting said fiber webs,

3. pressing the bonded webs to a predetermined thickness under pressure using an apparatus capable of conducting heating and pressing operations,

4. further bonding the bonded and pressed webs together by impregnating or filling the interstices remaining in the formed webs with a binder (b) without dissolving or swelling both the constituent fibers and the binder (a), and

4. dissolving the binder (a) to remove same from the product by using a solvent which dissolves the binder (a) but does not dissolve the constituent fibers and the binder (b), to thereby obtain a sheet of fibrous materials; said binder (a) being starch, dextrin, carboxymethyl cellulose, methyl cellulose, casein, polyethylene oxide, or polyvinyl alcohol and said binder (b) being polyvinyl chloride. polyvinyl acetate, polyamide, polyester, polyacrylate, polyurethane, synthetic rubber or natural rubber.

2. A process according to claim 1, wherein the amount of the binder (a) is such that after completion of the pressing, said binder (a) occupies from 0.5 to 10 percent of the total volume of the pressed webs.

3. A process according to claim 1, wherein the constituent fibers after completion of the pressing occupy from 12 to 40 percent ofthe total volume of the pressed webs.

4. A process according to claim 2, wherein the constituent fibers after completion of the pressing occupy from l2 to 40 percent of the total volume of the pressed webs. 

1. BONDING FIBER WEBS WITH ANOTHER USING A BINDER (A) HAVING PLASTICIZING OR MOLDING ABILITY AT A TEMPERATURE LOWER THAN A MELTING POINT OR DEGRADING TEMPERATURE OF THE FIBERS CONSTITUTING THE FIBER WEBS.
 2. BONDING FURTHER THE WHOLE WEBS TOGETHER BY IMPREGNATING OR FILLING THE INTERSTICES REMAINING WITH THE MOLDED WEBS WITH A BINDER (B) WITHOUT DISSOLVING OR SWELLING THE CONSTITUTENT FIBERS AD THE BINDER (A), AND
 2. pressing the bonded webs to a predetermined thickness under pressure using an apparatus capable of conducting heating and pressing operations,
 2. A process according to claim 1, wherein the amount of the binder (a) is such that after completion of the pressing, said binder (a) occupies from 0.5 to 10 percent of the total volume of the pressed webs.
 3. A process according to claim 1, wherein the constituent fibers after completion of the pressing occupy from 12 to 40 percent of the total volume of the pressed webs.
 3. further bonding the bonded and pressed webs together by impregnating or filling the interstices remaining in the formed webs with a binder (b) without dissolving or swelling both the constituent fibers and the binder (a), and
 3. DISSOLVING THE BINDER (A) TO REMOVE THEREFROM USING A SOLVENT WHICH DISSOLVES THE BINDER (A) BUT NOT THE CONSTITUTENT FIBERS AND THE BINDER (B). AS THE BINDER (A), THERE MAY BE USED STARCH, DEXTRIN, CARBOXYMETHYLCELLULOSE, METHYLCELLULOSE, CASEIN, POLYETHYLENE OXIDE, POLYVINYL CHLORIDE, POLYVINYL ALCOHOL, POLYVINYL ACETATE OR THE LIKE. AS THE BINDER (B), THERE MAY BE POLYVINYL CHLORIDE, POLYVINYL ACETATE, POLYVINYL ALCOHOL, POLYAMIDE, POLYESTER, POLYACRYLATE, POLYURETHANE, SYNTHETIC RUBBER OF EVERY KING, NATURAL RUBBER OR THE LIKE.
 4. dissolving the binder (a) to remove same from the product by using a solvent which dissolves the binder (a) but does not dissolve the constituent fibers and the binder (b), to thereby obtain a sheet of fibrous materials; said binder (a) being starch, dextrin, carboxymethyl cellulose, methyl cellulose, casein, polyethylene oxide, or polyvinyl alcohol and said binder (b) being polyvinyl chloride, polyvinyl acetate, polyamide, polyester, polyacrylate, polyurethane, synthetic rubber or natural rubber.
 4. A process according to claim 2, wherein the constituent fibers after completion of the pressing occupy from 12 to 40 percent of the total volume of the pressed webs. 